The invention concerns a method for the operation of a radio system and a system to execute the method.
Due to their difference in application, different technical norms with regard to transmitter frequencies, transmission journals, working ranges etc. were developed originally for mobile radio systems on the one hand and for radio systems for the purpose of wireless telephony on the other hand. This led to the fact that in most cases there is no compatibility between mobile radio systems, as they are for example used for automobile telephony, and the so-called CT systems (CT=cordless telephone), i.e. small-scale radio systems for wireless telephony.
Not always, but frequently, mobile radio systems (e.g. GSM systems) are cellular systems with a coverage area that is structured in a cell-like fashion. In each cell the mobile stations communicate via an air interface with a fixed base station. The base station can be connected with other cells of the same mobile radio system and/or other telecommunication system via suitable communication links (e.g. hard-wire telecommunication systems, beam links, radio links, etc.). Typical ranges of mobile radio systems (i.e. cell radii for cellular systems) are between a few km and about 60 km. In the case of cellular mobile radio systems, frequency allocation occurs usually based on active cell planning.
In contrast, CT systems usually comprise one or several fixed stations/parts which are hooked to the connection of a hard-wire fixed system, and one or several portable, wireless handsets or wireless telephones (portable parts) which can communicate with the fixed part via a radio interface. Typical ranges are between 50 m and several 100 m. Frequency allocation generally occurs with a dynamic, automatic procedure for frequencies that happen to be free at that time.
On the user side, there is a large need for a mobile telecommunication device, e.g. in the form of a hand mobile telephone which can be used both as a wireless telephone in one or several (small-scale) CT systems and as a mobile station for one or several (large-scale) mobile radio systems. Such a telecommunication device, which can be used in at least two different radio systems, is called a DMT (Dual Mode Terminal). Ideally the user of a DMT can always be reached at the same phone number, regardless which of the different radio systems he used to communicate with. This, however, depends heavily on the network support for such a service.
Several suggestions were submitted for the combined operation of large-scale mobile radio systems and small-scale radio systems. There are, for example, suggestions for the combination of a mobile radio system, according to the GSM standard, with a radio system operated in accordance with a standard developed for CT systems, particularly DECT.
For the production of relatively simple and inexpensive DMTs for the combined operation in a mobile radio system and a CT system, it is desirable that most of the components, such as antenna, receiver, transmitter etc., can be used for both the mobile radio system and the CT system. For this reason a more recent suggestion plans for the combination of a GSM mobile radio system with a CT system, which is operated according to a GSM norm modified for wireless telephony. A portion of the modification for this so-called GSM-CTS (CTS means xe2x80x9cCordless Telecommunication Systemxe2x80x9d) affects the GSM system control channels. The base station of a xe2x80x9cnormalxe2x80x9d GSM mobile radio system continuously transmits system-relevant data via special system control channels like identification of the base station, frequencies and channels used by the base station and possibly neighboring cells, etc. Much of this data is only required for the operation of a mobile radio system, but not for the operation of a CT system. To reduce the channel load, the so-called HBS (Home Base Station=fixed part or fixed station of a CT system operated according to GSM-CTS) therefore only emits system-relevant data required for CT operation instead of all GSM system control channels on a so-called beacon channel. Among other things, on the beacon channel an identification signal is transmitted continuously, based on which the DMTs can determine whether they are still in the coverage area of the HBS.
Mobile radio systems and wireless telephones have become more widespread over the last few years. Apart from speech transmission, newer systems also offer telefax and/or data transmission (e.g. computer communication). Although the frequency area made available for mobile radio systems and/or CT systems is relatively large by existing standards, capacity limits are already being met due to the wide-spread availability of these systems. We should therefore strive to use the limited resources of available frequency channels sparingly and use them efficiently.
For simplicity reasons, the terms xe2x80x9cfrequencyxe2x80x9d or xe2x80x9ccarrier frequencyxe2x80x9d are used in the following even if not only one, but actually a pair of so-called duplex frequencies or duplex carrier frequencies are used, e.g. to send from a base station to a mobile station (down-link) or vice versa (up-link). In the following, xe2x80x9cchannelxe2x80x9d means the resource that is required to transmit signals or user data via the air interface. In the GSM, for example, a channel consists of a combination of a certain carrier frequency and a certain time slot. A mobile telecommunication terminal is a telecommunication terminal (telephone, telefax machine, data transfer modem etc.) which sends and/or receives electromagnetic waves via an air interface for communication purposes. A mobile telecommunication terminal that can be used for at least two different radio systems is called a DMT (Dual Mode Terminal). A fixed station/fixed part is generally a typical fixed radio station, in the particular case of the CT system it is its fixed part. However, in the example of a car phone equipped for tandem operation the fixed part is not really fixed because the fixed station in this case consists of a part of the device that is fastened (fixed) in the car. The coverage area of a radio station is the area in which a mobile telecommunication terminal can communicate with the radio station via the air interface.
The invention is based on the task of making a method available for the operation of a radio system that ensures efficient utilization of a limited resource of available channels in a limited frequency range.
According to the invention, a method for the operation of a radio system includes muting a fixed station of the radio system when no operable mobile telecommunication terminal is located within the station""s coverage area. Muting by definition defines that no electromagnetic signals are sent via the transmitter, in particular this defines that no system-relevant data is sent via a beacon channel or a system control channel and no signals are sent for data or speech transmission i.e. that the transmitter of the fixed station is entirely muted. Preferably, a mobile telecommunication terminal that is capable to communicate with one or several other radio systems frequently monitors the busying of the channels by other radio systems. When this telecommunication terminal initially only sends on free channels itself and secondly informs the fixed station repeatedly of free and available channels on which it can transmit, then this would largely prevent that other radio systems with access to the same frequencies interfere with the radio system operated according to the method invented. In addition, other independent systems of the same type as well are not disturbed at all or only minimally. If there is no operable mobile telecommunication terminal any longer in the coverage area of the radio system""s fixed station, then no frequencies or channels are used by the radio system because the fixed station is being muted; the limited frequency bands are kept available for efficient utilization that is free from interferences.
In contrast to the invention, procedures used until now for the operation of radio systems do not provide for muting the transmitter of a fixed station as soon as no operable mobile telecommunication terminal is located in its coverage area. Procedures used in CT systems like DECT and GSM-CTS rather plan that the fixed station, transmits signals continuously via e.g., a system control channel or a beacon channel in order to signal to mobile telecommunication terminals the availability of the fixed station. If there is no operable mobile telecommunication terminal close to the fixed station, a portion of the available channels is thus continuously busied unnecessarily by the system control or beacon channel.
Furthermore, the utilization of channels by other radio systems can change during the extended absence of the mobile telecommunication terminal. A channel that was determined to be free at an earlier time with the help of the mobile telecommunication terminal may possibly not be available any longer. If such a channel is used as a beacon channel it can possibly cause considerable interference. The fixed station of the radio system can only determine this to a limited extent because only the signal of the base station of the other system allows for the most reliable evaluation and because the fixed station has no receiver for this signal for complexity and cost reasons.
A system to execute the procedure in accordance with the invention includes a fixed station for the radio system and a mobile telecommunication terminal suited to communicate with the radio system.
A fixed station in accordance with the invention has a circuit for the purpose of detecting an operable mobile telecommunication terminal in its coverage area and a circuit for the purpose of muting the transmitter of the fixed station, which is dependent on the state of the detection circuit.
A mobile telecommunication terminal in accordance with the invention has a circuit for the purpose of determining its position and examining whether that position is basically within the coverage area of a fixed station of the radio system with which it is entitled to communicate as well as a circuit for the purpose of registering the telecommunication terminal when the latter state occurs.
Preferably the method in accordance with the invention, includes the fixed station sending a identification signal via a pre-determined channel when there is at least one operable mobile telecommunication terminal in its coverage area in order to signal to the mobile telecommunication terminal the availability of the fixed station.
In the case of a preferred embodiment of the method in accordance with the invention, a mobile telecommunication terminal suited to communicate (via a radio interface) with the radio system determines its position from time to time and checks whether that is basically located within the coverage area of a fixed station of the radio system with which it is entitled to communicate. If this applies, the mobile telecommunication terminal checks whether there are free channels suited to communicate with the fixed station. If that applies as well, the mobile telecommunication terminal begins communicating with the fixed station by sending out signals to pre-determined channels, which the fixed station continuously monitors, and it tries to register with the fixed station. Successful registration is only possible when, among other things, the mobile telecommunication terminal is actually located within the coverage area of the fixed station and when the identification and authentication procedure integrated into the registration process is successful, i.e. when it is actually entitled to use the fixed station or the fixed station network. Not until at least one mobile telecommunication terminal has registered does the fixed station begin to send an identification signal. Due to the identification signal, the fixed station so-to-speak becomes visible to the mobile telecommunication terminal. Even after its registration with the fixed station, the mobile telecommunication device monitors the busying of channels by other radio systems in order to enable a transfer of the identification signal to another channel or a transfer of data channels, if necessary.
The mobile telecommunication terminal can use data from a cellular radio system, a locating system, such as GPS, Loran-C, Omega, or from any other system to determine its approximate position. Completely accurate position determination is not necessary because during the course of an applicable registration process it turns out whether the mobile telecommunication terminal is within the coverage area of the fixed station or not.
In one embodiment of the invention, the radio system consists of a CT system. The CT system can be operated according to a GSM-CTS, CT1, or DECT standard or any other standard suited for CT systems.
In a preferred embodiment of the invention, the mobile telecommunication terminal is suited to communicate with another radio system (the telecommunication terminal is therefore a DMT) and determines its position based on signals it receives from the other radio system. The other radio system can consist, for example, of a mobile radio system, particularly a GSM mobile radio system. To determine its position with the help of a GSM system, the base stations visible to the mobile telecommunication terminal, the relative delays of their signals, the field intensity of the signals and/or other data can be used. The two radio systems should preferably operate in an overlapping fashion, at least partially. If the two systems consist of e.g. a CT system and a GSM system and the DMT conducts its position determination based on the GSM data, the coverage area of each CT fixed station must overlap at least partially with one GSM cell because otherwise they cannot be xe2x80x98re-wakenedxe2x80x99 after an appropriate muting phase of the CT fixed station. Cells that are located entirely outside the other radio system can leave their beacon or broadcast channel turned on permanently because it does not interfere in this particular case.
The mobile telecommunication terminal preferably monitors the identification signal of the fixed station on a continuous basis after having registered with the fixed station in order to be able to recognize that a leaving of the fixed station""s coverage area is imminent based on a weakening of the identification signal. As soon as a leaving of the area is recognized based on the weakening of the identification signal, the mobile telecommunication terminal can cancel its registration with the fixed station. If the mobile telecommunication terminal is a DMT, the DMT will preferably only cancel its registration if it can register with another radio system at the same time. In the case of a DMT for a CT system and a GSM system, this e.g. prevents that the DMT cancels its registration with the CT system""s fixed station if it moves, for example, for a short time into a cellar where it is located neither in the CT system""s coverage area nor in the GMS system""s coverage area.
After successful registration with a fixed station, the mobile telecommunication terminal preferably monitors the identification signal of this fixed station and renews its registration from time to time, as long as it can recognizexe2x80x94based on the identification signalxe2x80x94that it is still located within the fixed station""s coverage area. Registration of the mobile telecommunication terminal with the fixed station is preferably canceled if it has not been renewed within the specified time frame since the last registration. This prevents mobile telecommunication terminals from remaining registered with the fixed station when they e.g. do not cancel correctly due to a sudden event.
With the invention, a method for operating a radio system as well as a system for executing this method are made available, which will ensure efficient usage of the channels in a limited frequency range. The method in accordance with the invention enables particularly the combined operation of a GSM mobile radio system with a CT system that is operated according to a GSM standard modified for the purpose of wireless telephony, with both systems utilizing the same limited frequency range reserved for GSM.
In connection with enclosed drawing, the following detailed description of the presented invention serves only as an example for a better understanding of the invention and is not to be regarded as a limitation to the scope of protection of the patent claims. The following description, combined with the enclosed drawing and the entire patent claims, will provide an expert undoubtedly with further advantageous embodiments and combinations of features, which are still within the range of the presented invention.